Treatment of material



2,830,881 Patented Apr. 15, 1958 TREATMENT @F MATERIAL Henry J. Wittroclr, (ipportunity, Wash, assignor to Kaiser Aluminum & Chemical Corporation, (Parkland, Calif., a corporation of Delaware No Drawing. Application January 25, M54 Serial No. 4%,tl9ll 9 Claims. (Ci. 23-230) .loys by any suitable means, e. g. hot dipping, there has been a need for a simple, inexpensive, and rapid method for determining the uniformity and thickness of the F coating. Such a method would facilitate desirable quality control and thereby assure a more satisfactory final product at a minimum of cost.

It is known that methods have been proposed in the past for determining uniformity of coatings on ferrous metal articles, e. g., the Preece test for galvanized metal (ASTM designation: A-239-41); In this test use is made of a solution of neutralized copper sulfate in which the coated metal is immersed for predetermined periods of time. Such a test, however, has been found completely unsatisfactory when applied to aluminized ferrous metal. In thecase of aluminized ferrous metal,

it is necessary that the solution composition be such that it will dissolve aluminum at a sufrlcientand steady rate,

similarly dissolve aluminum-iron intermetallic compound (where such compound is present), and clearly demarcate regions of aluminum, ferrous metal, and intermetallic compound. 1

Accordingly, it is a primary object of the invention t provide a novel composition and method for use in determining the uniformity of aluminum and aluminum alloy coatings on ferrous metal.

Another object of the invention is to provide a novel composition for use in determining the uniformity and thickness of aluminized coatings on ferrous metal which is characterized by its ability to dissolve the coating metal at a sufficient and steady rate and to clearly demarcate regions of coating metal and the ferrous metal.

A'further object of the invention is to provide a method for determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which is characterized by being simple and effective.

A further object of the invention is to provide a method for determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal, which method includes subjecting the coated metal to a plurality of immersions, each of substantially the same period of time, in the novel composition of the invention.

Other objects and advantages of the present invention will become apparent from the detailed description set forth below.

By the present invention there is provided a simple and effective means for determining uniformity and thickness of aluminum and aluminum alloy coatings wherein the coated ferrous metal is subjected to a series of immersions of predetermined periods of time in an aqueous 3 acid solution of predetermined composition whereby the herent and is not readily removed by brushing.

having a copper coating thereon.

if d presence of exposed portions of intermetallic compound, if any, and the ferrous metal can be readily detected to facilitate determination of coating uniformity and whereby the coating metal is dissolved at a predetermined rate thereby facilitating determination of coating thickness. 1 have discovered that coating uniformity and thickness can be readily determined by successively immersing the coated metal in an aqueous acid solution containing hydrogen ions, copper ions and fluoride ions as its essential active constituents in well-defined proportions and ranges of concentrations. The duration or period of time of each immersion should be substantially the same and the temperature of the solution maintained substantially constant in order to facilitate determination Y of the thickness of the coating on the basis of a predetermined rate of dissolution While at the same time facilitating determination of coating uniformity. The rate of dissolution in inches of coating thickness per unit time for a given coating metal, solution composition, and solution temperature is readily determined by subjecting a sample of the metal of given area to the action of the solution for a given period of time, determining the loss in weight due to dissolution, and converting this weight loss per unit area into inches of coating thickness dissolved per unit time.

As mentioned hereinabove, the period of time selected for immersion in any given case will result in a predetermined rate of dissolution of coating metal. When the coated ferrous metal is subjected to the first immersion the coating undergoes an electrochemical displacement reaction whereby a loosely adherent deposit of metallic copper is formed on the coating. After the predetermined immersion period has elapsed, the coated metal is withdrawn from the solution, rinsed in a suitable solution, e. g. water, to stop the reaction, and subjected to a wiping operation, e. g. brushing, which readily removes the loosely adherent copper deposit on the coating. The coated metal is thereafter subjected to successive immersions, rinses, and wiping until a point is reached where the deposited copper is firmly adherent and not removable by wiping. This point is where all of the coating metal and intermetallic compound, if present, has been dissolved and the copper deposit is on the ferrous surface. The thickness of the coating in any given area can then be determined by multiplying the number of immersion periods necessary to form an adherent copper deposit times the predetermined dissolution rate.

I have also found that the exposure of coating metal simultaneously with intermetallic compound and/ or with ferrous metal can be readily determined after any immersion and brushing operation. As mentioned hereinabove, the copper deposit which forms on the coating metal as a result of the electrochemical displacement reaction is loosely adherent and is readily removed by brushing. Where intermetallic compound is present and exposed to the action of the solution, the same result occurs as in the case of the coating metal. In the'case of the ferrous metal, however, the copper deposit is very ad- In addition, the exposure of coating metal, intermetallic compound and ferrous metal to the action of the solution gives rise to entirely different appearances after brushing, the coating metal being bright, the intermetallic compound being dark gray and matte, and the ferrous metal It will thus be seen that by practice of the invention the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal can be determined in a simple, effective manner.

As mentioned hereinabove, the solution of the present invention contains, as the essential active constituents, hydrogen ions, copper ions and fluoride ions. Hydrotion.

technique from one immersion to the next.

3 gen ions and hydrogen potentially available for ionization and dissociation are present in amounts from about 0.2 to 0.9% by weight of the solution and preferably are present in amounts from about 0.35 to 0.55% by Weight of the solution. The hydrogen ion concentration results in an acid solution equal to or more acid than a pH of about 2. Copper ions and copper potentially available for ionization and dissociation are present in amount at least about 0.35% by weight of the solution and preferably are present in amounts from about 0.9 to 2.5% by Weight of the solution. Fluoride ions and fluorine potentially available for ionization and dissociation are present in amounts from about 5 to 18.2% by weight of the solution and preferably are present in amounts from about 5.5 to 8.5% by weight of the solu- It is to be understood that such ions may be supplied in the form of various compounds as long as their concentrations are maintained within the required range.

The proper hydrogen ion concentation for the acid solution may be maintained by the use of hydrofluoric acid in an amount of from about 3.8 to 18% by weight of the solution. When using 52% HF, this amount corresponds to a volume concentration of from about 65 to 320 cc. per liter. The preferred hydrogen ion concentration is preferably maintained by the use of hydrofluoric acid in an amount of from about 7.0 to 11.2% by weight of the solution which corresponds to a volume concentration of from about 120 to 195 cc. per liter of 52% HF. Although hydrofluoric acid is the preferred source of hydrogen ions, other acids whose anions are compatible with the solution may be used as, for example, sulfuric acid, phosphoric acid, sulfamic acid, etc.

The copper ions may be introduced in the solution in the form of copper fluoride in an amount at least about 0.76% by weight of the solution and preferably in an amount from about 2 to 5.4% by weight of the solution. In terms of copper fluoride calculated as CuF -2H O, these amounts are equivalent to at least about 11 and preferably from about to grams per liter. The copper ions may also be introduced in other suitable forms such as copper sulfate.

The fluoride ion concentration of the solution is maintained by the use of hydrofluoric acid and copper fluoride or equivalent constituents in the above-mentioned amounts.

It is to be understood that the fluoride ions may be introduced, in part or in whole, in forms other than copper fluoride crystals and in forms other than hydrofluoric acid, to avoid handling of the highly corrosive acid. For example, ammonium fluoride and ammonium bifiuoride may advantageously be used as sources of fluoride ions. In such cases, other suitable sources of hydrogen and copper ions may be used. For example, as set forth above, sulfuric acid could be used as the hydrogen ion source and copper sulfate could be used as the copper ion source.

Thus the composition of the present invention essentially comprises an aqueous acid solution containing hydrogen, copper and fluoride ions in amounts which are equivalent to that supplied by from about 3.8 to 18% (preferably 7.0 to 11.2%) hydrofluoric acid and at least about 0.76% (preferably 2 to 5.4%) copper fluoride calculated as CuF -2H O by weight of solution.

The chemical bath is preferably operated at temperatures from about to F. and immersion periods of about one minute duration are preferably used. It has been found that the use of this temperature range and period of immersion makes the test easily controllable and productive of consistent results. It is to be understood, however, that shorter or longer immersion periods may be used. Shorter immersion times generally give a more clear picture of coating uniformity and a closer determination of coating thickness. In such cases, however, greater care is required in maintaining the identical On' the other LII hand, if the duration of immersion is too great, there is a tendency for an excessive amount of the coating and intermetallic compound (if present) to be dissolved thereby making a satisfactory determination of coating thickness and uniformity difficult. Although the temperature of the bath is preferably 75 to 85 C., it will be understood that the bath temperature may be lower or higher. The use of lower temperatures tends to slow down the reaction while the use of higher temperatures speeds up the reaction. Generally it is found that the higher the bath temperature the shorter must be the period of each immersion and vice versa in order to facilitate a satisfactory determination of coating uniformity and thickness.

To illustrate the composition of the invention the following examples are given. It is to be understood, however, that the purpose of these examples is merely illustrative in nature, and should in no way be construed as a limitation on the scope of the invention.

Weight Percent Constituent Volume Concen- Ooncen- Weight tration,cc./liter tratton, of

g./]1ter Solution It will thus be seen that by the present invention there is provided a composition and method for determ imng the uniformity and thickess of aluminum and aluminum alloy coatings on ferrous metal which is simple and effective. It will be understood that various alterations, changes and modifications may be made to the present invention without departing from the spirit and scope thereof as defined by the appended claims wherein:

What is claimed is:

1. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersions of substantially the same period of time in an aqueous acid bath containing hydrogen ions and hydrogen potentially available for ionization and dissociation in amount from about 0.2 to 0.9% by weight of solution, copper ions and copper potentially available for ionization and dissociation in amount at least about 0.35% by weight of solution, and fluoride ions and fluorine potentially available for ionization and dissociation in amount from about 5 to 18.2% by weight of solution, said solution having a pH not in excess of about 2, said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of said coating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number .of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate.

2. A method according to claim 1 wherein the solution is maintained at a temperature of from about 75 to 85 F. and wherein the period of time for each immersion is about 1 minute.

3. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersions of substantially the same duration in an aqueous acid bath containing hydrogen ions and hydrogen potentially available for ionization and dissociation in amount from about 0.35 to 0.55% by weight of solution, and copper ions and copper potentially available for ionization and dissociation in amount from about 0.9 to 2.5% by weight of solution, and fluoride ions and fluorine potentially available for ionization and dissociation in amount from about 5.5 to 8.5% by weight of solution, said solution having a pH not in excess of about 2, said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of said coating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate.

4. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersions of substantially the same period of time in a heated aqueous acid bath containing hydrogen, copper, and fluoride ions in amount equivalent to that supplied by from about 3.8 to 18% hydrofluoric acid and at least about 0.76% copper fluoride calculated as CuF -2H O by weight of solution, said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of said coating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate. 5. A method according to claim 4 wherein hydrogen copper and fluoride ions are present in amounts equivalent to that supplied by from about 7.0% to 11.2%hydrofiuoric acid and 2 to 5.4% copper fluoride calculated as CuF -ZH O by Weight of solution.

6. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersons of about 1 minute duration each in an aqueous acid bath essentially comprising about 7.3% HP and about 4.7% copper fluoride calculated as CuF -2H O by weight of solution, and maintaining the solution at a temperature of from about 75 to 85 F.,

said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of said coating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate.

7. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersions of about 1 minute duration each in an aqueous acid bath essentially comprising about 21.2% H SO about 11.2% NH F, and about 3.8% copper fluoride calculated as CuF -ZH O by weight of solution, and maintaining the solution at a temperature of from about 75 to 85 F., said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of said coating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate.

8. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersions of about 1 minute duration each in an aqueous acid bath essentially comprising about 21.2% H about 11.2% NH F, and about 3.8% copper sulfate calculated as CuSO -5H O by weight of solution, and maintaining the solution at a temperature of from about 75 to F., said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of said coating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate.

9. A method of determining the uniformity and thickness of aluminum and aluminum alloy coatings on ferrous metal which comprises subjecting the coated metal to a plurality of immersions of about 1 minute duration each in an aqueous acid bath essentially comprising about 21.2% H2804, about 11.2% NH4HF2, and about 3.8%

copper sulfate calculated as CuSO '5H O by weight of solution, and maintaining the solution at a temperature of from about 75 to 85 F., said bath dissolving the coating metal at a predetermined rate per immersion period and providing a loosely adherent deposit of copper on the coating metal and a firmly adherent deposit of copper on exposed ferrous metal, rinsing said coated metal after each immersion to stop the dissolution action by said bath and removing loosely adherent copper deposit formed during each immersion, and continuing said cycle of operations until a firmly adherent copper deposit is provided on said ferrous metal, the uniformity of saidtcoating being determined by the presence simultaneously of loosely adherent and firmly adherent copper deposits and the thickness of said coating being determined for any given area thereof by multiplying the number of immersion periods necessary to form a firmly adherent copper deposit times said predetermined dissolution rate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF DETERMINING THE UNIFORMITY AND THICKNESS OF ALUMINUM AND ALUMINUM ALLOY COATINGS ON FERROUS METAL WHICH COMPRISES SUBJECTING THE COATED METAL TO A PLURALITY OF IMMERSIONS OF SUBSTANTIALY THE SAME PERIOD OF TIME IN AN AQUEOUS ACID BATH CONTAINING HYDROGEN IONS AND HYDROGEN POTENTIALLY AVAILABLE FOR IONIZATION AND DISSOCIATION IN AMOUNT FROM ABOUT 0.2 TO 0.9% BY WEIGHT OF SOLUTION, COPPER IONS AND COPPER POTENTIALLY AVAILABLE FOR IONIZATION AND DISSOCIATION IN AMOUNT AT LEAST ABOUT 0.35% BY WEIGHT OF SOLUTION, AND FLUORIDE IONS AND FLUORINE POTENTIALLY AVAILABLE FOR IONIZATION AND DISSOCIATION IN AMOUNT FROM ABOUT 5 TO 18.2% BY WEIGHT OF SOLUTION, SAID SOLUTION HAVING A PH NOT IN EXCESS OF ABOUT 2, SAID BATH DISSOLVING THE COATING METAL AT A PREDETERMINED RATE PER IMMERSION PERIOD AND PROVIDING A LOOSELY ADHERENT DEPOSIT OF COPPER ON THE COATING METAL AND A FIRMLY ADHERENT DEPOSIT OF COPPER ON EXPOSED FERROUS METAL, RINSING SAID COATED METAL AFTER EACH IMMERSION TO STOP THE DISSOLUTION ACTION BY SAID BATH AND REMOVING LOOSELY ADHERENT COPPER DEPOSIT FORMED DURING EACH IMMERSION, AND CONTINUING SAID CYCLE OF OPERATIONS UNTIL A FIRMLY ADHERENT COPPER DEPOSIT IS PROVIDED ON SAID FERROUS METAL, THE UNIFORMITY OF SAID COATING BEING DETERMINED BY THE PRESENCE SIMULTANEOUSLY OF LOOSELY ADHERENT AND FIRMLY ADHERENT COPPER DEPOSITS AND THE THICKNESS OF SAID COATING BEING DETERMINED FOR ANY GIVEN AREA THEREOF BY MULTIPLYING THE NUMBER OF IMMERSION PERIODS NECESSARY TO FORM A FIRMLY ADHERENT COPPER DEPOSIT TIMES SAID PREDETERMINED DISSOLUTION RATE. 